JP5531640B2 - Feed control device for machine tools - Google Patents

Description

  The present invention relates to a feed control device for a machine tool that controls the feed of a moving table such as a moving spindle head or tool post, or a moving table serving as a machining head in a drilling machine in a machine tool such as a lathe.

  In a machine tool such as a lathe, feed control of a moving platform such as a movable spindle stock and a tool post is generally feedback controlled using a detection value of a position detector such as a pulse coder provided in a servo motor. . Moreover, in a machine tool, thermal expansion and thermal deformation of the bed and other parts occur due to cutting heat and heat generation of parts due to machine operation. Such thermal expansion and thermal deformation lead to a decrease in processing accuracy. Some of them are equipped with a cooling device as a countermeasure. However, in order to sufficiently suppress the thermal expansion, the cooling device becomes large, and the processing accuracy cannot be ensured only by cooling. For this reason, various types have been proposed in the past that use thermal measurement, a linear scale, or the like to measure thermal expansion and correct thermal displacement such as the cutting depth of a tool.

JP 2002-144191 A

  However, in thermal displacement correction by temperature measurement, it is difficult to perform accurate thermal displacement correction because it depends on the complexity, uncertainty, environment, etc. of the conversion calculation to thermal displacement. In addition, in the case of using a conventional linear scale, since the entire movable stroke range is measured, accuracy such as resolution of the scale must be obtained for the entire movable stroke range. In addition, the temperature characteristics of the scale itself are also affected. There is no linear scale that can measure with high accuracy over a long stroke range, and even if manufactured, it is expensive. For these reasons, accurate thermal displacement correction is difficult.

An object of the present invention is to provide a feed control device for a machine tool that can accurately correct thermal displacement with a simple configuration, perform high-precision machining, and suppress an increase in cost for ensuring accuracy. Another object of the present invention is to enable accurate thermal displacement correction with a much simpler configuration.
Still another object of the present invention is to enable efficient and accurate thermal displacement correction when a plurality of workpieces are repeatedly processed to the same shape.
Still another object of the present invention is to enable accurate thermal displacement correction with a simple configuration when machining one workpiece.

  A feed control device for a machine tool according to the present invention controls a moving table that is installed so as to be movable forward and backward with respect to a base and supports a workpiece or a tool, an advance / retreat driving mechanism that moves the moving table forward and backward, and the advance / retreat driving mechanism. In a machine tool comprising a feed control means, a linear scale having a local scale range along the moving direction of the moving table is provided on one of the base and the moving table, and the other of the base and the moving table. Further, a sensor for reading the linear scale is provided. The “base” is not limited to the bed, and may be a base that is fixed in position relative to the moving base, and may be a base that moves relative to the bed. Further, the “moving table” is not limited to the one that directly supports the workpiece or the tool, but may be a table that supports the workpiece or the tool by an object that is movably mounted on the moving table.

  According to this configuration, a linear scale having a local scale range along the moving direction of the moving table is used. Since the scale range is short, a linear scale capable of performing highly accurate measurement can be obtained at low cost. Even with such a linear scale having a local scale range, appropriate thermal displacement correction can be performed by appropriately designing the position of the scale range. Therefore, the thermal displacement can be corrected with a simple configuration with high accuracy, high-precision machining can be performed, and an increase in cost for ensuring accuracy can be suppressed.

Before Symbol feed control means is adapted to position control of the driving source according to the detected value of the position detector for detecting a position of the moving base provided on the driving source of the reciprocating drive mechanism, to the feed control unit, that having a correction means for correcting the detected value of the position detector by a detection value of the sensor read the linear scale. The position detector provided in the drive source is a pulse coder provided integrally with the drive source, a rotary encoder connected to the drive source, or the like.
In the case of this configuration, basically, the position of the drive source is controlled according to the detection value of the position detector provided in the drive source. In performing this position control, the correction means performs correction using the detected value read with the linear scale in the local scale range. This correction is offset correction of the origin position of the position detector. In this way, basically, a position detector normally provided in the drive source is used, and the correction is performed with a linear scale in the local scale range, so that accurate thermal displacement correction can be performed with a simpler configuration. It becomes possible.

In the case where the correcting means is provided, the machine tool performs a repetitive cycle in which a plurality of workpieces are sequentially transferred and carried in and the same processing is performed on the plurality of workpieces, and the correcting means performs the repetitive cycle. Among them, the correction at the time of machining the current workpiece may be performed by the detection value of the sensor that has read the linear scale at the time of machining the previous workpiece.
The temperature of the machine tool does not rise or fall abruptly and hardly changes after a few minutes. On the other hand, when the same machining is repeatedly performed on a plurality of workpieces, the machining time for one workpiece is generally as short as several seconds to several tens of seconds, for example. Therefore, accurate correction can be performed by using the detection value of the sensor that has read the linear scale at the time of machining the previous workpiece for correction. In addition, when machining the previous workpiece, the movable table is always located at the position where the tool is in contact with the workpiece, and a dedicated cycle for measurement using the linear scale is performed separately from the machining cycle. There is no need to provide it. Therefore, it is possible to efficiently and accurately correct the thermal displacement by measuring at the time of machining the previous workpiece.

In the case where the correction unit is provided, the machine tool executes a measurement cycle in which the linear scale is read by the sensor before actual machining of the workpiece, and the correction unit is configured to execute the measurement cycle. The correction may be performed during actual machining based on the detected value.
In the case of high-mix low-volume machining, etc., by executing the measurement cycle immediately before machining in this way, the measurement cycle time is required, but accurate thermal displacement correction can be performed.

A feed control device for a machine tool according to the present invention controls a moving table that is installed so as to be movable forward and backward with respect to a base and supports a workpiece or a tool, an advance / retreat driving mechanism that moves the moving table forward and backward, and the advance / retreat driving mechanism. In a machine tool comprising a feed control means, a linear scale having a local scale range along the moving direction of the moving table is provided on one of the base and the moving table, and the other of the base and the moving table. in the set only the sensor for reading the linear scale, the feed control means, the position control of the driving source according to the detected value of the position detector for detecting a position of the moving base provided on the driving source of the reciprocating drive mechanism is intended to, in the feed control means, order to have a correction means for correcting the detected value of the position detector by a detection value of the sensor read the linear scale, simple Configuration can be done accurately temperature compensation, the high-precision machining is performed, it is possible to suppress the increase in cost for ensuring accuracy.

The feed control means is provided in a drive source of the advance / retreat drive mechanism and controls the position of the drive source according to a detection value of a position detector that detects the position of the moving table. because of the detection value of the sensor read the linear scale having a correction means for correcting the detected value of the position detector, can be performed with good accuracy temperature compensation in more simple structure.

  The machine tool performs a repetitive cycle in which a plurality of workpieces are sequentially exchanged and carried in, and the plurality of workpieces perform the same machining on each other, and the correction means performs the previous work in the repetitive cycle. When the correction at the time of machining of the current workpiece is performed based on the detection value of the sensor that has read the linear scale at the time of machining, the thermal displacement is efficiently and accurately performed when machining the same shape on a plurality of workpieces repeatedly. Correction can be made.

  The machine tool executes a measurement cycle in which the linear scale is read by the sensor before actual machining of the workpiece, and the correction means performs the correction during actual machining based on a detection value at the time of execution of the measurement cycle. In the case of performing a thermal displacement correction with a simple configuration with high accuracy when machining one workpiece.

It is a block diagram which shows the conceptual structure of the machine tool provided with the feed control apparatus of the machine tool which concerns on 1st Embodiment of this invention. It is a perspective view which shows an example of the machine tool main body of the machine tool. It is a front view of the linear scale of the machine tool. It is explanatory drawing of the arrangement | positioning relationship between the linear scale of the machine tool, and a workpiece | work. It is a block diagram which shows the conceptual structure of the machine tool provided with the feed control apparatus of the machine tool which concerns on 2nd Embodiment of this invention. It is explanatory drawing of the arrangement | positioning relationship between the linear scale of the machine tool, and a workpiece | work.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing the overall conceptual configuration of a machine tool provided with this machine tool feed control device. The machine tool includes a machine tool main body 1 that processes a workpiece W, a transport device 2 that loads and unloads the workpiece W with respect to the machine tool main body 1, and a machine tool control device 3. The machine tool control device 3 includes a machine tool main body control device 4 that controls the machine tool main body 1 and a transport control device 5 that controls the transport device 2.

  As shown in FIG. 2, in the illustrated example, the machine tool main body 1 is a main spindle moving type lathe, and a main spindle 9 is mounted on a main spindle base 8 installed on a bed 6 serving as a base via a moving base 7. Is supported rotatably, and a tool post 10 is installed on a bed 6 via a support base 11. The support base 11 is fixed to the bed 6 and installed. The tool post 10 is formed of a turret and is supported on the support base 11 so as to be capable of rotational indexing.

  The moving table 7 is installed on the X axis guide 12 provided on the bed 6 so as to be movable in the horizontal main axis radial direction (X axis direction) orthogonal to the axis O of the main axis 9. The X-axis advance / retreat drive mechanism 15 including a drive source 13 such as an installed servo motor and a feed screw mechanism 14 for converting the rotation output into a linear motion is driven to move back and forth. The headstock 8 is installed on a Z-axis guide 16 provided on the moving base 7 so as to be movable in the main shaft axis direction (Z-axis direction), and a drive source 17 such as a servo motor installed on the moving base 7. It is driven forward and backward by a Z-axis advance / retreat drive mechanism 19 comprising a feed screw mechanism 18 (FIG. 1) and its rotation output converted into linear motion. The spindle 9 is driven to rotate by a spindle motor 20 installed on the spindle base 8. A chuck 21 is detachably provided at the front end of the main shaft 9. The chuck 21 can grip the workpiece W (FIG. 1) by a plurality of chuck claws 21 a that move in the chuck radial direction.

  The tool post 10 is rotatable around a horizontal rotation center T along the X-axis direction with respect to the support base 11, and has a plurality of tool mounting portions arranged in the circumferential direction on the outer peripheral portion. A tool 23 such as a tool or a rotary tool is attached to each tool attachment portion via a tool holder 22. In the figure, only one tool 23 is shown, and the other tools 23 are not shown. The tool post 10 is pivotally indexed to a position where an arbitrary tool 23 faces the main shaft 9 by an indexing motor (not shown). The tool post 10 has a front shape of a circle as illustrated, or a polygonal shape.

  In FIG. 1, the machine tool main body control device 4 includes a computer-type numerical control device and a programmable controller, and has an arithmetic control unit 32 that decodes and executes a machining program 31 formed of an NC code or the like. The arithmetic control unit 32 processes a movement command (not shown) of the machining program 31 and instructs the control means 33, 34, and 35 of each axis (X axis, Z axis, and main axis) composed of a servo controller or the like. A value is given, and the sequence control command of the machining program 31 is transferred to the sequence control means 36. The sequence control means 36 is means for controlling a sequence operation such as opening and closing of the chuck 21 in the machine tool body 1. As the control means 33, 34, 35 for each axis, an X-axis feed control means 33, a Z-axis feed control means 34, and a spindle control means 35 are provided. The spindle control means 35 is means for controlling the spindle motor 20 (FIG. 2).

  The conveyance control device 5 is a computer-type control device, and has an arithmetic control unit 39 that decodes and executes the conveyance program 38. The conveyance control device 5 transmits and receives signals for completion and start of each operation to and from the machine tool control device 4, and controls the loading and unloading of the workpiece W to and from the spindle chuck 21 by the conveyance device 2 in synchronization with the machine tool main body 1. .

The X-axis feed control means 33 is a means for giving a position command to the drive source 13 of the X-axis advance / retreat drive mechanism 15 so that the moving base 7 moves to the command position sent from the arithmetic control unit 32. Feedback control is performed using the detection signal of the position detector 13 a provided in the source 13.
The Z-axis feed control means 34 is a means for giving a position command to the drive source 17 of the Z-axis advance / retreat drive mechanism 19 so that the headstock 8 moves to the command position sent from the arithmetic control unit 32. Feedback control is performed using a detection signal of a position detector (not shown) provided in the source 17.

The X-axis feed control means 33 has a correction means 37 that performs correction based on a detection signal from a specific position detector 42 including a linear scale 40 and a sensor 41.
The linear scale 40 has a scale range 40a in a local range along the moving direction (X-axis direction) of the moving table 7, and is installed on the bed 6 as a base. More specifically, it is provided on the X-axis guide 12 of the bed 6. A sensor 41 that reads the linear scale 40 is installed on the movable table 7. The specific position detector 42 including the linear scale 40 and the sensor 41 may be magnetically detected or optically detected, but in this example, a magnetically detected one is used. ing.

  The scale range 40a that is a local range of the linear scale 40 is, for example, a range of 1 to 10 mm, and in the illustrated example, a range of 5 mm. The linear scale 40 has mounting portions 40b extending to both sides of the scale range 40a, and is attached by a fixing tool such as a screw provided in the mounting portion 40b and inserted through the mounting hole 40ba. The material of the linear scale 40 is preferably a material having a small linear expansion coefficient, such as Invar or quartz glass.

  The installation position of the sensor 41 is, for example, the same X-axis direction position as the axis O of the main shaft 9. The installation position of the linear scale 40 may be an arbitrary position. For example, the linear scale 40 is linearly arranged so that the center of the reading range 40a comes to a position separated from the cutting edge of the tool 23 by the radius of the outer diameter of the workpiece W having a specific diameter. The scale 40 is attached to the bed 6. That is, the linear scale 40 is attached to the bed 6 so that the center of the reading range 40a comes when the cutting edge of the tool 23 comes into contact with the outer peripheral surface of the workpiece W having the correct outer diameter. The workpiece W having the specific diameter is, for example, an arbitrary workpiece among workpieces that are sequentially exchanged with the machine tool and repeatedly subjected to the same machining.

  The correction means 37 of the X-axis feed control means 33 reads the linear scale 40 when the sensor 41 passes the scale range 40a of the linear scale 40, and an error from the reading value of the X-axis position detector 13a at the time of reading. Correction for offsetting the position command value output by the X-axis feed control means 33 is performed by an amount corresponding to the amount. At this time, the correction means 37 obtains a value of one specific point (for example, the center point of the reading range 40a) from the reading value of the sensor 41. For example, an average value of values obtained by reading the entire scale range 40a may be obtained as a specific single point value, or only one specific point in the scale range 40a may be detected. Thus, the value outside the setting range may be ignored, and the position of a specific point may be obtained by performing statistical processing such as obtaining an average value or a median value from only the values within the setting range.

  The above error is, for example, the following value. If the sensor 41 is installed at the same position in the X-axis direction as the spindle axis O as described above and there is no thermal displacement, the position of the position detector 13a when the position of a specific point of the linear scale 40 is detected. The reading value is determined by the correcting means 37 so that the specific one point (for example, the center point of the reading range 40a) and the spindle center O are the same position, that is, “zero”, but it is not “zero”. If an error has occurred, the error is regarded as an error from the reading value of the position detector 13a when the linear scale 40 is read. The correction means 37 performs correction for offsetting the read value of the position detector 13a by the error thus obtained or by a value obtained by multiplying the error by an arbitrarily determined coefficient.

  When the correction means 37 uses the read value of the linear scale 40, it varies depending on the processing or conveying mode of the workpiece W, and the like. For example, a case will be described in which the machine tool 1 executes a repetitive cycle in which a plurality of workpieces W are sequentially exchanged and carried out and the same processing is performed on the plurality of workpieces W. In this case, the correction means 37 performs the correction at the time of machining of the current workpiece W based on the detection value of the sensor 41 that has read the linear scale 40 at the time of machining of the previous workpiece W in the repetition cycle.

  Before the actual machining of the workpiece W, the machine tool 1 may execute a measurement cycle in which the linear scale 40 is read by the sensor 41. In this case, the correction means 37 performs the correction at the time of actual machining based on the detection value at the time of execution of the measurement cycle. In the correction means 37, the operator may set the reading value of the linear scale 40 corresponding to any of the above-mentioned forms in the correction means 37 before starting, or the conveyance control device. Any signal output from 5 may be detected and selected.

  According to the feed control device of the machine tool, the linear scale 40 having the local scale range 40a along the moving direction of the moving table 7 is used, and the scale range 40a is short, so that high-precision measurement can be performed. The linear scale 40 can be obtained at low cost. Even with such a linear scale 40 having a local scale range 40a, appropriate thermal displacement correction can be performed by appropriately designing the position of the scale range 40a. Therefore, the thermal displacement can be corrected with a simple configuration with high accuracy, high-precision machining can be performed, and an increase in cost for ensuring accuracy can be suppressed.

In particular, as described above, the installation position of the sensor 41 is set to the same X-axis direction position as that of the spindle axis O, and the installation position of the linear scale 40 is set by the radius of the outer diameter of the workpiece W having a specific diameter from the cutting edge of the tool 23. When the center of the reading range 40a is located at a distant position, it is possible to realize processing with higher accuracy. This is because the position of the movable table 7 affects the machining accuracy because it is the position of the movable table 23 when the tool 23 is in contact with the workpiece W for machining.
Since the correction means 37 is provided, basically, the position detector 13a normally provided in the drive source 13 is used and the correction is performed by the linear scale 40 in the local scale range 40a. Thus, accurate thermal displacement correction can be performed with a simpler configuration.

  When the correction means 37 performs correction at the time of machining of the current workpiece W by the detection value obtained by reading the linear scale 40 at the time of machining of the previous workpiece W in a repeated cycle in which a plurality of the same machining is performed, Efficient and accurate thermal displacement correction can be performed. The temperature of the machine tool 1 does not rise or fall rapidly, and hardly changes after a few minutes. On the other hand, when the same machining is repeatedly performed on a plurality of workpieces W, the machining time for one workpiece W is generally as short as several seconds to several tens of seconds, for example. Therefore, accurate correction can be performed by using the detection value of the sensor 41 that has read the linear scale 40 when processing the previous workpiece W for correction. Further, when machining the previous workpiece W, the movable table 7 is always located at the position where the tool 23 is in contact with the workpiece W and machining, and a dedicated cycle for measurement by the linear scale 40 is machined. There is no need to provide it separately from the cycle. Therefore, it is possible to efficiently and accurately correct the thermal displacement by measuring at the time of processing the immediately preceding workpiece W.

  In order to read the linear scale 40 by the sensor 41 when machining the previous workpiece W in a plurality of repeated cycles in which the same machining is performed, for example, in each machining cycle of the workpiece W, the sensor 41 A process of passing through the linear scale 40 may be added.

When the correction means 37 performs the correction at the time of actual machining based on the detection value at the time of execution of the measurement cycle for measuring the workpiece W before machining immediately before the machining cycle, the measurement cycle time is required, but a small amount of various products Accurate thermal displacement correction can be performed in the case of processing or the like.
Measuring cycles for measuring the workpiece W before processing immediately before, such as sensor 41 until the tool 23 contacts the workpiece W passes through the linear scale 40, when the diameter of the workpiece W is relatively small (W in FIG. 1 _S Can be measured in the approach process until the tool 23 comes into contact with the workpiece W, and it is not particularly necessary to move the movable table 7 for the measurement cycle. On the other hand, when the diameter of the workpiece W is relatively large (indicated by W _L), the sensor 41 until the tool 23 contacts the workpiece W arrives the linear scale 40, can not pass, as the measurement cycle, the workpiece W the tool 23 A measurement cycle in which the sensor 41 passes through the linear scale 40 by the movement of the movable base 7 in the X-axis direction after the spindle base 8 is moved so that the Z-axis direction does not interfere with the Z-axis direction is provided.

  In the first embodiment, the sensor 41 is disposed on the spindle axis O. However, for example, as in the second embodiment shown in FIG. The scale of the linear scale 40 may be a position where the sensor 41 can read the scale in a state where the moving table 7 is at the position where 23 is in contact. In this embodiment, since it is a spindle moving type and the tool 23 is fixed in position, the linear scale 40 is attached so that the cutting edge position Q of the tool 23 is located at the center of the scale range 40a. Further, in this embodiment, the machine tool 1 performs outer diameter cutting of the cylindrical workpiece W having a specific outer diameter, and is biased toward the tool 23 from the spindle axis O by the radius of the outer diameter. The sensor 41 is attached to the movable table 7 so that the center of the detection surface of the sensor 41 is located at the above position. Therefore, the scale of the linear scale 40 can be read by the sensor 41 in a state where the moving table 7 is at a position where the tool 23 comes into contact with the workpiece W and is processed.

  In this case, the above error is, for example, the following value. When there is no thermal displacement, the read value of the position detector 13a when the position of one specific point of the linear scale 40 is detected is that one specific point (for example, the center point of the read range 40a) is from the spindle center O. Although it should be the value of the biased distance, if an error has occurred with respect to this biased distance, the error is regarded as an error from the reading value of the position detector 13a when reading the linear scale 40. The correction means 37 performs correction for offsetting the read value of the position detector 13a by the error thus obtained or by a value obtained by multiplying the error by an arbitrarily determined coefficient.

  In particular, when the linear scale 40 is installed at a position where the scale of the linear scale 40 can be read by the sensor 41 at the position of the moving table 7 when the tool 23 is in contact with the workpiece W as described above. Therefore, it is possible to realize highly accurate processing. This is because the position of the movable table 7 affects the machining accuracy because it is the position of the movable table 23 when the tool 23 is in contact with the workpiece W for machining.

  In the above embodiment, the linear scale 40 is attached to the bed 6 which is the base, and the sensor 41 is attached to the moving base 7. Conversely, the linear scale 40 is attached to the moving base 7 and the sensor 41 is attached to the moving base 7. It may be attached to the bed 6. Moreover, although the said embodiment demonstrated about the case where it applied to the spindle moving type | mold lathe whose main axis | shaft 9 moves to a perpendicular | vertical biaxial direction, the main stage 8 moved to the X-axis direction, and the tool post 10 moved to the Z-axis direction. It can also be applied to a spindle moving lathe. In that case, the “moving base” referred to in the claims corresponds to the moving head stock 8, and the linear scale 40 is attached to one of the head stock 8 and the bed 6, and the sensor 41 is attached to the other. Further, the present invention can be applied not only to a spindle moving type lathe but also to a tool post moving type lathe. In that case, the turret or the pedestal on which the turret is mounted and moved is the “moving pedestal” referred to in the claims. Furthermore, the present invention can be applied not only to a lathe but also to a machine tool such as a milling machine or a drilling machine, as in the case of a lathe.

DESCRIPTION OF SYMBOLS 1 ... Machine tool main body 4 ... Machine tool main body control apparatus 5 ... Conveyance control apparatus 6 ... Bed (base)
DESCRIPTION OF SYMBOLS 7 ... Moving stand 8 ... Spindle base 9 ... Spindle 10 ... Tool post 12 ... X-axis guide 13 ... Drive source 13a ... Position detector 15 ... X axis advance / retreat drive mechanism 21 ... Chuck 23 ... Tool 31 ... Machining program 32 ... Calculation Control unit 33 ... X-axis feed control means 37 ... Correction means 40 ... Linear scale 40a ... Scale range 40b ... Mounting part 41 ... Sensor O ... Spindle axis Q ... Cutting edge position W ... Workpiece

Claims (3)

In a machine tool provided with a movable base that is installed so as to be able to move forward and backward with respect to the base and supports a workpiece or a tool, an advance / retreat drive mechanism for moving the movable base forward and backward, and a feed control means for controlling the forward / backward drive mechanism. to either the base and the moving base, the provided movable carriage linear scale local scale range along the movement direction of the base and the moving base while setting the sensor for reading the linear scale The feed control means controls the position of the drive source according to a detection value of a position detector that is provided in the drive source of the advance / retreat drive mechanism and detects the position of the moving table. the feed control device of the machine tool characterized that you have a correction means for correcting the detection value of the position detector by a detection value of the sensor read the linear scale. The machine tool performs a repeated cycle in which a plurality of workpieces are sequentially exchanged and carried in, and the plurality of workpieces are subjected to the same machining, and the correction means is configured to perform the previous workpiece in the repeated cycle. feed control device of the detected value of said sensor that has read the linear scale when the processing of a machine tool according to claim 1, wherein performing the correction in processing of this work. The machine tool executes a measurement cycle in which the linear scale is read by the sensor before actual machining of the workpiece, and the correction means performs the correction during actual machining based on a detection value at the time of execution of the measurement cycle. The machine tool feed control device according to claim 1, wherein:

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